Over the last two decades there has been a significant evolution in coatings technology for wood finishing applications. For many years, the demands for increased production levels and consistent product quality and increasing labor costs caused industry researchers to focus on the development and use of solvent-based coating formulations. Although there has been a significant effort directed toward the development of water-based emulsion coatings as replacement for traditional solvent-based coating formulations, water-based coatings have found little acceptance and use in the wood finishing industry. That is due in part to the fact that production managers are hesitant to change existing solvent-based finishing schedules which have not only proven to provide consistent product quality, but have also been developed to do so with optimum cost efficiency. Moreover, those skilled in the wood finishing art know that water-based coatings not only suffer the inherent disadvantages of freezing in cold weather, corroding containers, and supporting bacterial growth, but they are also known to complicate, even compromise, control of finish quality. Surface hue/color is more difficult to control in water-based finishing protocols because of migration of natural and applied stains into the finish coatings. Further, water-based coatings are known to produce a characteristic rough surface due to a phenomenon referred to in the art as "grain raising". Wood fibers in the surface of the wood absorb water and swell in the presence of the water-borne coating composition. Thereafter, the wood fibers shrink as they dry resulting in wrinkles/roughness in the finished wood surface. In spite of all those problems presented by the use of water-based coatings in the wood finishing industry, proposed state and federal legislation, and promulgation of air quality rules by state and federal agencies, are requiring the wood finishing industry to find ways to use water-based coatings in wood finishing protocols as a means for reducing use and release of volatile organic compounds (VOCs).
It is one object of this invention to provide a process for treating or pretreating wood surfaces to reduce or eliminate grain raising associated with the application of water-based wood finishing compositions.
It is another object of this invention to provide a pretreatment for wood surfaces intended to be stained and coated with one or more non-pigmented water-based coating formulations.
In a further embodiment, this invention provides a novel wood stain composition for use in wood finishing protocols utilizing water-based sealers and/or topcoats.
In still another aspect of this invention there is provided a method for reducing grain raising in wood surfaces prone to exhibit such condition when finished with water-based finish coating compositions.
Another embodiment of this invention provides a veneer treatment process and processed veneer which can be finished utilizing water-based finish coating compositions without associated grain raising and resultant surface roughness.
Those and other embodiments of this invention are accomplished by a wood pretreatment process including the step of wetting the surface of a wood substrate with a solution of an effective amount of aluminum salt. Preferably the aluminum salt solutions are acidic (pH&lt;7) and contain about 1 to about 15 weight percent of an aluminum salt. In wood finishing protocols requiring application of a stain, it is preferred that the stain be applied to the surface prior to the treatment in accordance with this invention, or at the same time utilizing the novel water-based, aluminum salt-containing, stain compositions of this invention. The invention finds application in industrial manufacturing operations, such as furniture manufacture, requiring production of high quality wood finishes. The process of the present invention can be implemented within the framework of most existing wood finishing protocols with little, if any, additional equipment and/or labor cost.
The invention also finds application in pretreatment of veneer destined for use in the manufacture of furniture, cabinetry and other high quality wood finish applications. Veneer can be treated in accordance with this invention and delivered in a pretreated state to manufacturers using water-based finishing protocols.